Multilayer catheter balloon

ABSTRACT

A method of producing laminated inflatable, substantially inextensible expander members having composite properties enhancing their use on intravascular catheters, such as angioplasty catheters is described. Diverse polymeric compounds of differing properties are coextruded to create a multilayer parison. The parison is subsequently drawn and expanded in a blow molding operation to yield an expander member exhibiting enhanced properties including lubricity, burst-strength, limited radial expansion, bondability, and rupture characteristics.

BACKGROUND OF THE INVENTION

[0001] I. Field of the Invention

[0002] This invention relates generally to balloon catheters, and moreparticularly to a method for fabricating a multi-layer balloon compositeexhibiting enhanced characteristics attributable to the properties ofthe individual layers.

[0003] II. Discussion of the Prior Art

[0004] As an alternative to open-heart, coronary bypass surgery, atechnique referred to coronary transluminal angioplasty has beendeveloped following the pioneering introduction of the technique by A.Gruntzig. In carrying out this procedure, a dilatation catheter havingan inflatable expander member (balloon) on the distal end thereof isrouted through the vascular system to a location within a coronaryartery containing a stenotic lesion. Following placement of the expandermember across the lesion, a fluid is introduced into the proximal end ofthe catheter and is used to inflate the expander member to apredetermined relatively high pressure whereby the lesion is compressedinto the vessel wall restoring patency to the previously occludedvessel.

[0005] It is desirable that the composite expander member exhibit thefollowing characteristics:

[0006] 1. High burst (tensile) strength;

[0007] 2. Low radial expansion at elevated pressures;

[0008] 3. Ease of bonding to a catheter body;

[0009] 4. Failure characteristics avoiding pinhole ruptures; and

[0010] 5. Low coefficient of friction.

[0011] The Schjeldahl et al. U.S. Pat. No. 4,413,989 owned byapplicants' assignee discloses a coronary transluminal angioplastycatheter in which the expander member is formed from polyethyleneterephthalate in a drawing and blow molding process so as to providebiaxial orientation to the material. Such PET balloons are found toexhibit the desirable property of high burst strength and relatively lowradial expansion when inflated to seven atmospheres or more. However,because the catheter body itself is generally fabricated from aformulation containing silicon rubber, polyethylene, PET orpolyurethane, a problem exists when attempts are made to bond theexpander member to the distal end portion of the catheter body. The PETpolyester balloon tends not to adhere easily to the catheter bodyespecially in a thermal bonding process.

[0012] Moreover, experience with polyethylene, PVC and polypropyleneexpansion members has shown that at relatively high pressures, pinholeleaks form which may create a high velocity jet of inflation fluidcapable of perforating the blood vessel when it impinges on the vesselwall. Thus it would be desirable if the expander member can befabricated in such a way that it exhibits a controlled mode of failure,i.e., a rapid rupture so that the pressure is released over asignificant area in a short time frame.

SUMMARY OF THE INVENTION

[0013] The above-listed desirable characteristics are achieved inaccordance with the present invention by forming a multi-layer balloonwhere the individual layers afford a desirable property to thecomposite. It has been found that a layer of medium or relatively highmelt temperature material which also exhibits high tensile strength withrelatively low distensibility can be used to provide the required highburst or tensile strength and low radial expansion at high pressuresrequired by the expander member in a composite structure. This layer maybe referred to as the tensile layer or tensile ply. It may be abiaxially-oriented film of relatively high crystallinity.

[0014] In the composite structure, the tensile layer is combined as anouter layer with a chemically and physically compatible adhesion orbonding inner layer which is fabricated from materials having superiorglue bonding or melt bonding characteristics. The bonding layer alsomust have good interlayer adhesion characteristics with the materialused for the tensile layer. The bonding layer imparts the necessaryadhesion properties to properly bond the expander member to the distalend portion of the catheter body. If melt bonding is the desired mode,the material of the bonding layer should have a lower melting point thanthat of the tensile layer so that melt bonding of the composite may bereadily achieved in the fabrication process with minimal effect on thetensile ply. In this regard, it should be noted that the bonding layermay or may not be continuous or coextensive with the entire innersurface of the tensile layer inasmuch as it is required generally onlyin the vicinity of the expander/catheter interface surfaces.

[0015] Examples of materials exhibiting the required high tensile, lowdistensibility and having medium melt temperatures include certaincopolymers such as ABS (acrylonitrile-butadiene-styrene), ABS/nylon,ABS/polyvinyl chloride (PVC) and ABS/polycarbonate. Such materialshaving high melt temperatures include acrylonitrile copolymer,polyacrylamiede, polyacrylate and polyacrylsulfone. Other materialshaving suitable characteristics include high melt temperature polyesterssuch as polyethylene terephthalate (PET), polybutylene terephthalate(PBT), polyethylene naphthalate (PEN), liquid crystal polymer (LCP),polyester/polycaprolactone and polyester/polyadipate; and high melttemperature polyethers including polyetheretherketone (PEEK),polyethersulfone (PES), polyetherimide (PEI) and polyetherketone (PEK),polymenthylpentene, polyphenylene ether, polyphenylene sulfide, andstyrene acrylonitrile (SAN). It should be noted that LCP has a very highmelt temperature and SAN, a lower melt temperature than the other listedpolyethers. Additional compounds having the required tensile propertieswhich have a medium melt temperature include polyamides such as nylon 6,nylon 6/6, nylon 6/66, nylon 6/9, nylon 6/10, nylon 6/12, nylon 11 andnylon 12.

[0016] Suitable adhesion materials for the bonding layer having a highdistensibility but excellent melt bond and glue adhesion properties withrelatively low melt temperatures include ethylene, propylene, ethylenevinylacetate and ethylene vinyl alcohol (EVA), various ionomers,polyethylene type I-IV, polyolefins, polyurethane, polyvinyl chloride,and polysiloxanes (silicones). Those with low to medium melttemperatures include fluorocarbons such as polychlorotriethylene (CTFE),poly[ethylene-co-chlorotrifluoroethylene] (ECTFE) copolymer ethylenetetrafluoroethylene (ETFE), copolymer tetrafluoroethylene andhexafluoropropylene (FEP), perfluoroalkane (PFA) and poly[vinylidenefluoride] (PVDF).

[0017] It will be appreciated that the particular combination chosenwould depend on the particular application and particular catheterinvolved, and that an array of multilayer expanders of differentcomposition combinations particularly applicable to different situationscan be produced. In addition, specific properties required foraddressing a specific stenosis could be utilized to produce atailor-made expander.

[0018] More particularly with respect to the process, a tubular parisonis first generated in a co-extrusion process whereby different polymericmaterials are coaxially layered. Subsequently, the parison is insertedin a blow molding fixture, allowing the tube to be longitudinally drawnand radially expanded until the composite film is oriented, the maximumO.D. of the expander member is defined and a desired film thickness isachieved. For example, in forming the parison, PET of a predeterminedviscosity may be coextruded with polyethylene where, forming theparison, the polyethylene lines the lumen thereof. When the expandermember is formed from the parison in the blow molding operation, the PETlayer affords the desired burst strength and limited radial expansioncharacteristic while the polyethylene layer enhances the ability to bondthe resulting balloon to the catheter body.

[0019] The characteristic of lubricity may also be added by coating theexterior of the composite with a suitably lubricious plastic exhibitinghigh hydrophilic characteristics. Suitable lubricious hydrophilicmaterials include polycaprolactam polyvinylindol, N-vinylpyrrolidone,various hydrogels, and other hydrophilic lubricious polymeric materials.

[0020] One successful embodiment of the system of the invention utilizesa combination of polyethylene terephthalate (PET) as the tensile layerin combination with a bonding layer of polyethylene. The compositePET/polyethylene balloon was coated on the exterior of the PET withpolycaprolactam. By forming a three-layer tubular parison having a layerof plastic with known rupture characteristics, the polyethylene layermay provide the bondability attribute, the PET, the limited radialexpansion characteristic and/or the controlled rupture characteristicwhile polycaprolactam again affords the lubricity.

[0021] Of course, the known rupture or failure characteristics involvethe failure by bursting or large scale rupture of the tensile layerrather than the development of small or pin hole leaks in which a smallstream of high pressure fluid is released. This minimizes possibledamage to surrounding tissue caused by high pressure fluid leakage fromthe membrane.

DESCRIPTION OF THE DRAWINGS

[0022] The various features, characteristics and advantages of theinvention will become apparent to those skilled in the art from thefollowing detailed description of a preferred embodiment, especiallywhen considered in conjunction with the accompanying drawings in which:

[0023]FIG. 1 is a process flow chart illustrative of the presentinvention;

[0024]FIG. 2 is a partial schematic illustration of apparatus formanufacturing parisons in a co-extrusion process;

[0025]FIG. 3 is a cross-sectional view of a two-component co-extrusiondie useful in forming a two-layer parison;

[0026]FIG. 4 illustrates schematically an apparatus for blow molding theparison into a biaxially oriented multilayer expander member;

[0027]FIG. 5 shows the expander joined to the distal end of a catheter;and

[0028]FIG. 6 depicts an alternative embodiment of the multilayerexpander member.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] With reference to FIG. 1, in fabricating the multilayer expandermember in accordance with the present invention, the first step in theprocess is to create a parison which when heated and then drawn andblown creates a balloon or expander member for use on an intravascularcatheter. The extruding apparatus is indicated generally by numeral 10in FIG. 2 and is seen to comprise a motor 12 coupled in drivingrelationship to a gear box 14 whose output shaft comprises acoarse-pitched archimedian screw 16 rotating within a heated barrel 18.In accordance with known practice, the screw generally has threedistinct sections. In the “feed” section 20, directly beneath the feedhopper 22, the screw channel depth is constant and relatively large andserves to convey solid polymer material from the hopper. The depth ofthe flute in the “compression” section 24 is uniformly tapered anddesigned to compact the plastic and force it into contact with thebarrel 18 to enhance melting. The melting is achieved mainly by acombination of heat conducted from electrical heating elements 26contained in the barrel and the heat generated by the intense shearingin the molten layer formed between the barrel and the solid material.Numeral 28 identifies the “metering” section of the screw in which theflute depth is constant and relatively small. It controls the outputfrom the extruder in terms of quantity, steadiness and homogeneity.Disposed at the end of the screw 16 is an extruder die 30 which, in thecase of the present invention, provides for co-extrusion of at least twodifferent plastics. The first plastic passing through extruder 10combines with a second plastic exiting a substantially identicalextruder shown schematically at 32 to create a concentrically layeredtubular parison, the cross-section of which is seen in the view of FIG.4.

[0030]FIG. 3 is a cross-sectional view taken through a two-portco-extrusion die. For example, the output from the metering section 28of the extruder 10 may be fed into die port A in FIG. 3 while that fromthe metering section of the screw of extruder 32 feeds port A. Themolten plastic flows together to form a layer with the plastic enteringport B surrounding the plastic entering port A. As the plastic is madeto flow through the die, air is also introduced through the central bore34 of the die 30 to prevent the collapse of the tubular shaped exudate.

[0031] In accordance with one aspect of the invention, the plasticentering port A, for example, may comprise a polyolefin or PVC whilethat forced into port B may be a homopolyester, preferably PET, of apredetermined viscosity. With these two constituents, the resultingtubular parison will have the PVC as the inner tubular layer and the PETas its outer layer. The thickness of the individual layers will bedetermined by the mass flow ratios provided by the respective extruders.The final diameter of the parison is determined by the size of the dieexit opening, the total flow of material into ports A and B and thetake-away or draw speed.

[0032] The balloon itself is fabricated in a blow molding operationwherein the parison 40 is inserted into the blow mold 42 as shown inFIG. 4 and air or other suitable fluid is introduced through the port 44at a predetermined pressure. The mold 42 has a cavity 46 correspondingto the desired size of the balloon to be produced.

[0033] After the tubular parison is disposed in the mold, the mold isheated to thereby raise the tubing temperature to a point between thesecond order transition temperature and the first order transitiontemperature of the polyester polymer.

[0034] Of course, the inner layer can be caused to adhere to and attachthe balloon to the exterior of the tubular catheter body in any desiredmanner. The material of the inner layer may be such that relatively lowmelt temperature material can be utilized to achieve a permanent meltbond. Preferably, the exterior of the tubular catheter body is providedwith a coating of the same or similar material to that of the innerlayer of the multilayer balloon structure such that the materials bondedare substantially identical. This also allows the continuous joint to bemade utilizing melt bonding the materials. In this regard, it is desiredthat the material forming the bonding layer of the multilayer systemhave a melting temperature sufficiently below that of the material ofthe tensile layer so that the melt bonding can be achieved withoutaffecting the future physical characteristics of the system.

[0035] As described above, it is desirable that the expander memberitself exhibits rather high tensile strength properties. This meansexhibiting a burst pressure well in excess of 7 atmospheres whileundergoing a radial expansion less than about 3-10 percent. The actualstrength, of course, will depend on the relative tensile strength of thematerial and thickness of the material layer. In addition, theseextruded materials are ones not prone to pinhole leaks in the process ofthe invention in most cases results in a mode of failure, should failureoccur, in the form of a rapid rupture which releases the internalpressure over a considerable area in a short time frame so that damageto the vessel is minimized.

[0036] By first drawing the tubular parison and subsequently blowmolding same, biaxial orientation takes place whereby the PET layer 56,while remaining flexible, becomes strong as regards the inflationpressure at which the material will burst. When it is desired to bondthe finished balloon onto the catheter body as illustrated in FIG. 5,the inner layer 48 of PVC can readily be bonded to an outer PVC tubularbody 50 and to an inner tubular body 52, such as by adding adhesive 54between the outer layer 56 and the inner layer 48. The space between thecoaxially disposed tubes allows for injection of a balloon inflationfluid. Balloons produced in accordance with the invention may exhibit aburst pressure well in excess of 7 atmospheres while radially expandingless than about 3-10 percent. While the PVC layer 48 adds little to theburst strength of the composite, it does facilitate the attachment ofthe balloon to the exterior of the tubular catheter body.

[0037] If it is desired to increase the lubricity of the compositeballoon, this may be accomplished by dipping or other coating themultilayer balloon in a suitable hydrophilic material such aspolyvinylidol, N-vinylpyrolodone, hydrogels, etc.

[0038] With reference to FIG. 6 and rather than utilizing PET incombination with PVC, a balloon having enhanced properties maybe createdby co-extruding a high molecular weight crystalline polyester 60 with alower molecular weight amorphous polyester 62 in forming the parison. Anouter layer of filled polymer 64 adds lubricity. As known in the art,adhesive 66, 68 may be juxtaposed between layers 60, 62 and 64.Following drawing and radial expansion in a blow molding operation, theresulting balloon is found to exhibit high burst strength, low radialexpansion and superior bondability as compared to conventional PETsingle-layer balloons.

[0039] The rupture characteristics of a polymer layer can be modified toincrease the rupture rate by adding filler material. The fillermaterials may be an inert type, such as calcium carbonate, generally inpowder form, carbon in fiber form, or an incompatible second phasepolymer. Incompatible phase polymer systems afford many advantageouscharacteristics and are a function of the dispersion between the twophases. Materials which might be candidates for this are polypropyleneand selected rubbers, polyester and polypropylene.

[0040] This invention has been described herein in considerable detailin order to comply with the Patent Statutes and to provide those skilledin the art with the information needed to apply the novel principles andto construct and use such specialized components as are required.However, it is to be understood that the invention can be carried out byspecifically different equipment and devices, and that variousmodifications, both as to the equipment details and operatingprocedures, can be accomplished without departing from the scope of theinvention itself.

1-25 (Canceled)
 26. A method of producing a laminated expander member,the method comprising: coextruding different polymeric materials to forma multilayer parison comprising a first layer comprising a firstpolymeric material including a liquid crystal polymer, and a secondlayer comprising a second polymeric material different from the firstpolymeric material; and forming the parison into the expander member.27. The method of claim 26, further comprising coextruding a third layerdisposed towards an exterior of the expander member relative to thefirst and second layers, the third layer enhancing the lubricity of theexpander member.
 28. The method of claim 26, further comprisingbiaxially orienting the first layer.
 29. The method of claim 26, whereinthe first layer consists essentially of liquid crystal polymer.
 30. Themethod of claim 26, wherein the second layer is an adhesion layer. 31.The method of claim 30, wherein the adhesion layer is disposed towardthe interior of the expander member relative to the first layer.
 32. Themethod of claim 26, wherein the expander member has a radial expansionnot exceeding three percent when inflated to seven atmospheres.
 33. Themethod of claim 26, wherein forming the parison into the expander membercomprises drawing the parison and expanding the parison in a blowmolding operation.